The present invention relates to an improved fluid pump, particularly for connection to the blood circulatory system of a living being.
The pump according to the invention has thus primarily been developed for use as an extracorporeal blood pump in conjunction, for instance, with surgical operations, dialysis, oxygenation of the blood in patients having an impaired lung function, for circulatory support after a cardiac insufficiency or for victims of accidents with heart or lung injuries, etc. It is also conceivable, however, for a pump according to the invention to be constructed in a manner which would enable it to be implanted in a patient as an artificial heart. It is also possible that a pump according to the invention could be advantageous to use also in other contexts, such as regional organ perfusion and/or organ perfusion in vitro.
Extracorporeal blood pumps used today for the above mentioned purposes are in the great majority of cases peristaltic so-called roller pumps, in which the blood is transported through a tube by rollers compressing the tube and simultaneously moving therealong. Recently a type of pulsatile pump has also begun to be used to a certain extent for the mentioned purposes, which pump basically consists of a pump bladder with flexible, resilient walls, which bladder has inlets and outlets provided with non-return valves and is enclosed in a surrounding rigid chamber, inside which a periodically varying pressure is generated for alternate compression and expansion of the pump bladder.
The peristaltic roller pumps have the serious drawback that it is very difficult to avoid considerable damages to the blood corpuscles in the pumped blood in consequence of the squeeze and shear forces that the blood corpuscles are subjected to in the pump.
The peristaltic roller pumps as well as the pulsatile pumps of the above mentioned type also have the common drawback that the operation of the pump will cause considerable subpressures at the inlet of the pump, and also in the pump bladder in the case of the pulsatile pump, if the inflow of blood to the pump inlet does not correspond to the nominal pumped flow of the pump but falls below it. Such a situation is liable to occur with relative ease, for example as a result of a blockage at the end of the catheter connecting the pump to a blood vessel, for instance by abutment of the catheter end with the wall of the blood vessel. The subpressure which in the hitherto used pumps in such cases is automatically generated on the inlet side of the pump and in the pump bladder may give rise to very troublesome problems. Thus, the subpressure may cause serious mechanical damages to the patient's blood vessels. Further, the subpressure may cause air to leak into the pump system through untight connections between various parts of the pump system, and if the subpressure is sufficient it may also result in gas being released from the pumped blood. In both cases serious gas emboli may occur. In the prior art blood pumps of the type discussed it is therefore necessary to monitor the pressure prevailing on the inlet side of the pump and in case of a subpressure intervene into the operation of the pump such that no serious situation may arise. Such a monitoring and control system will, of course, complicate and raise the price of the pump and will in itself constitute an additional source of possible malfunctions.
An attempt to avoid the above mentioned problems in roller and peristaltic pumps is disclosed in DE-C-3420861, describing a pump tubing made of a soft flexible material such that at a slight overpressure the tubing will take a form permitting throughflow of a fluid, and at a subpressure in relation to the ambient pressure the tubing will immediately collapse.
The basic construction and principle of a fluid pump of the type to which the present invention relates is described in WO 87/03492 (the disclosure of which is incorporated by reference herein).